A new pathological lesion, vimentin metaplasia, was discovered to be associated with the preneoplastic and neoplastic phenotype of renal tubular epithelial lesions in F344 rat kidney. The transition to the vimentin phenotype appeared to be a prerequisite for neoplastic transformation by several genotoxic carcinogens and tumor promoters. A novel mouse lung tumor model was discovered and developed. N-nitrosobis(2-chloroethyl)urea was found to induce hyperplastic, preneoplastic and neoplastic lesions arising within bronchioles. Tumors of similar cellular origin are found in human lung. This new model could play a role in the study of the etiology, pathogenesis, and therapy of comparable human tumors. An animal model for the study of myoepithelial tumors of epithelial tissues was found and described. Mouse mammary tumors with significant myoepithelial components were induced in B6D2F1 and D2B6F1 mice by 7,12-dimethylbenz[a]anthracene. Transplantable myoepithelial tumors were established and provided an important model for studying myoepithelial differentiation and biology. Rhesus monkeys infected with SIV/Delta developed a unique giant cell enteritis, not previously described. Also, B cell lymphomas and a pancreatic carcinoma were found in these monkeys. The lymphomas were always associated with marked lymphoid hyperplasia.